1. Field of the Invention
This invention relates generally to intervertebral spinal surgery, and more particularly to surgical instrumentation and to a method for creating one or more spaces between adjacent vertebral bodies in which the space has a shape and vertebral surfaces adapted in size to receive an implant or implants to be implanted in the space, and the method of implanting those implants.
2. Description of the Prior Art
The spinal disc that resides between adjacent vertebral bodies maintains the spacing between those vertebral bodies and, in a healthy spine, allows for relative motion between the vertebrae. With disease and/or degeneration a disc may become painful and/or mechanically insufficient warranting surgical fusion across the affected disc. Where fusion is intended to occur between adjacent vertebral bodies of a patient""s spine, the surgeon typically prepares an opening at the site of the intended fusion by removing some or all of the disc material that exists between the adjacent vertebral bodies to be fused. Because the outermost layers of bone of the vertebral endplate are relatively inert to new bone growth, the surgeon must work on the endplate to remove at least the outermost cell layers of bone to gain access to the blood-rich, vascular bone tissue within the vertebral body. In this manner, the vertebrae are prepared in a way that encourages new bone to grow onto or through an implant that is placed between the vertebrae. An implant or insert may or may not promote fusion of the adjacent vertebral bodies, may be an artificial spinal disc, may permit surface ingrowth, and may be made of bone or inert material, such as titanium. All of these examples and more are implants.
Present methods of forming this space between adjacent vertebrae generally include the use of one or more of the following: hand held biting and grasping instruments known as rongeurs; drills and drill guides; rotating burrs driven by a motor; and osteotomes, chisels, and scraping implements. Surgeons often prefer a drilling technique due to its being ease, quick, and accurate. Sometimes the vertebral endplate must be sacrificed as occurs when a drill is used to drill across the disc space and deeper into the vertebrae than the thickness of the endplate. Such a surgical procedure is typically used to prepare a space in the spine for an implant having a circular cross section and necessarily results in the loss of the hardest and strongest bone tissue of the vertebrae, the endplate, and thereby robs the vertebrae of that portion of its structure best suited to absorbing and supporting the loads placed on the spine by everyday activity. Where the surgeon chooses to forego drilling a large bore across the disc space in an attempt to preserve that good bone he must nevertheless use one of the above instruments to work upon the endplates of the adjacent vertebrae to access the vascular, cancellous bone that is capable of participating in the fusion and causing active bone growth, and also to attempt to obtain an appropriately shaped surface in the vertebral bodies to receive the implant, which means and method are unreliable for that purpose.
There exists therefore a need for an improved surgical instrumentation and a related method for providing a space that is non-circular in cross section, and preferably a substantially quadrilateral space across the height of a disc space and into the adjacent surfaces of the adjacent vertebral bodies while taking advantage of the safe, easy, and accurate technique of boring or drilling into the spine to form a space and to shape the adjacent endplates to receive implants not typically associated with boring techniques.
Accordingly, it is an object of the present invention to permit the formation of a substantially quadrilateral space in a spine for inserting a spinal implant into a disc space between adjacent vertebral bodies.
Yet another object is to provide surgical instrumentation for preparing an interbody space to receive a spinal implant and a related method for working upon vertebral body endplates adjacent a disc space useful in any region of the human spine, specifically, the cervical, dorsal, or lumbar regions.
Additional objects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims.
To achieve the objects and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention comprises a surgical instrument set for use in spinal surgery for forming a substantially quadrilateral space in the spine for implanting a spinal implant into a disc space between adjacent vertebral bodies and the methods for doing so.
An embodiment of the present invention includes an instrument set including a spinal marker for marking a location on the spine. The marker has a shaft and a disc penetrating extension extending from the shaft for insertion into the disc space between adjacent vertebral bodies. The shaft may have any number of cross sections including rectangular and circular. The marker preferably includes a shoulder for abutting against the exterior of the adjacent vertebral bodies. The disc penetrating extension of the marker preferably is tapered to facilitate insertion into the disc space. The shaft of the marker has a proximal end and an opposite distal end oriented toward the spine. The shaft of the marker preferably includes a passage having a dye receiver at the proximal end of the shaft of the marker and at least one dye exit hole at the distal end of the shaft of the marker for marking the spine. The marker preferably includes means for coupling to a syringe.
The instrument set includes a guard having an opening for providing protected access to the disc space and the adjacent surfaces of the vertebral bodies adjacent the disc space and having a disc penetrating extension extending from the guard for insertion into the disc space between the adjacent vertebral bodies and for bearing against the adjacent vertebral endplates of the adjacent vertebral bodies. The guard may have two disc penetrating extensions extending from the guard and diametrically opposed to each other. The disc penetrating extensions preferably has a leading-edge that may include either of a pointed, tapered, radiused, chamfered, or wedge tipped shape to ease insertion of the extensions into the disc space. The guard preferably is adapted to conform at least in part to the exterior of the adjacent vertebral bodies. The guard may include a shoulder that conforms at least in part to the exterior of the adjacent vertebral bodies. The shoulder preferably curves to correspond to the external curvature of the adjacent vertebral bodies. The guard may further include means for engaging the adjacent vertebral bodies when in use. The guard includes a hollow shaft adapted to allow access through the hollow shaft to the disc space.
The instrument set further includes a guide for guiding a bone removal device. The guide has a shaft adapted for insertion into the guard. The guide includes means for guiding the formation of the substantially quadrilateral space across the height of the disc space and into the adjacent surfaces of the adjacent vertebral bodies. The guiding means preferably includes a plurality of guide bores. The plurality of guide bores may overlap one another. The plurality of guide bores may include three guide bores, and in particular may include a main guide bore and two secondary guide bores located to a side of the main guide bore. The main guide bore and the two secondary guide bores preferably are oriented such that the bores formed in the spine through the main guide bore and the two secondary guide bores form a first hole pattern, which when the guide is rotated 180 degrees and used to form a second hole pattern, the overlapping first and second hole patterns form the substantially quadrilateral space.
Another embodiment of the present invention further includes a secondary guide having a shaft adapted to be inserted into the guard. The secondary guide preferably includes means for guiding the formation of a bore centrally oriented within the space to be formed. The centrally oriented bore preferably contacts opposite sides of the substantially quadrilateral space to be formed.
The instrument set may also include a bone compactor having a shaft adapted for insertion into the guard. The shaft terminates in a compaction end. The compaction end preferably has an upper surface and a lower surface that presses upon the adjacent vertebral endplates of the adjacent vertebral bodies. The compaction end preferably has either a rectangular, trapezoid, or quadrilateral cross-section, or any other shape corresponding to the desired cross-section of the space to be formed in the spine. The compaction end may be any of beveled, radiused, or tapered to ease introduction of the bone compactor into the space. The bone compactor may have a trailing end having a dimension greater than the shaft to prevent over penetration of the bone compactor into the guard. Alternatively, the instrument set may include a tool having a sharpened leading end so as to formalize the flattening of the vertebral surfaces.
An embodiment of the invention also comprises a method for creating a substantially quadrilateral space in a spine for inserting a spinal implant into a disc space between adjacent vertebral bodies, comprising the steps of: positioning a guard into contact with the adjacent vertebral bodies for protecting access to the disc space and the adjacent vertebral bodies; and boring, through the guard, a plurality of bores across the disc space to form the substantially quadrilateral space across the height of the disc space and generally into the adjacent surfaces of the adjacent vertebral bodies, rather than deep into the vertebral bodies themselves.
An embodiment of the present invention may include the step of marking the spine for guiding, by reference marks, the proper location of the guard. The step of marking preferably includes inserting a penetrating extension of a spinal marker into a central point of the disc space between the adjacent vertebral bodies. An-embodiment of the present invention includes the step of placing dye spots on the spine by injecting the dye through openings in a shaft of the spinal marker. The depth of penetration of the marker into the disc space is controlled.
An embodiment of the method of the present invention includes the step of distracting the disc space between adjacent vertebral bodies, and in particular, the distracting step may include the step of inserting a distractor having a disc penetrating extension into the disc space between adjacent vertebral bodies and against endplates of the adjacent vertebral bodies. The depth of penetration of the distractor into the disc space is preferably controlled. The method may further include the step of changing disc penetrating extensions of the distractor in accordance with a desired distractor distance between adjacent vertebral bodies. The guard may be inserted over the distractor in the disc space, and then the distractor may be removed from within the guard.
The positioning step may include inserting at least one disc penetrating extension extending from the guard into the disc space between the adjacent vertebral bodies for bearing against endplates of the adjacent vertebral bodies. The insertion of the disc penetrating extension into the disc space in one embodiment of the preferred invention distracts the adjacent vertebral bodies. Another method of the present invention further includes the step of controlling a depth of penetration of the extension into the disc space. Another embodiment of the present invention includes the step of engaging the guard with the adjacent vertebral bodies through prongs extending from the guard and into the adjacent vertebral bodies.
The boring step may include the sub-step of using a template in association with the guard. The template may be rotated 180 degrees along its longitudinal axis. The boring step may include the sub-step of using either of a drill, mill, laser, burr, grinder, or other means to bore the plurality of bores. The plurality of bores may overlap. The boring step may include forming at least three bores in the spine to form a first bore pattern, and in particular may include forming at least a main bore and at least two secondary bores located to a side of the main bore. The main bore has a diameter that is preferably greater than a diameter of each of the two secondary bores. The main bore in the spine is preferably positioned to form a portion of three sides of the substantially quadrilateral space formed in the spine. Each of the two secondary bores are preferably positioned to form a portion of two adjacent sides of the substantially quadrilateral space formed in the spine. A second bore pattern having at least three bores in the spine may be formed such that the first and second bore patterns defined the substantially quadrilateral space. The substantially quadrilateral space may be one of a substantially rectangular shape and a substantially trapezoidal shape. Further a central bore can be utilized to increase the width of the space formed. The described xe2x80x9cquadrilateral spacexe2x80x9d is defined to cover a space that is actually a generally flat upper and flat lower surface having a height therebetween that is symmetrical from side to side and that may be uniform from front to back or may be such that these opposed surfaces are in angular relationship to each other from front to back; to the extent that the sides of the space are located within the disc space and not the bone of the vertebral bodies their specific shape is not important, and need not be planar.
Further the invention may comprise the step of inserting a multiple passage drill guide into the guard to guide the formation of those bores. The guide may be inserted into the guard for guiding the forming of the first bore pattern. The invention may further include the steps of removing the guide from the guard, rotating the guide 180 degrees along its longitudinal axis, reinserting the guide into the guard, and forming, through the plurality of openings in the guide, a second bore pattern, the first and second bore patterns defining the substantially quadrilateral space. The invention may further include the step of controlling the depth of penetration of the guide into the guard.
Yet another embodiment of the present invention includes the step of compressing outer edges of the substantially quadrilateral space. The step of compressing preferably includes inserting a compactor having a compaction end through the guard and into the substantially quadrilateral space formed in the spine. The step of compressing may also include inserting a bone chisel compactor having a sharpened cutting edge for cutting bone. The depth of penetration of the compactor into the disc space is preferably controlled. The step of compressing may include the sub step of inserting a spinal implant through the guard and into the substantially quadrilateral space formed in the spine to compress the outer edges on the substantially quadrilateral space.
Another embodiment of the present invention includes a surgical method to prepare a segment of a human spine having a disc and two vertebrae adjacent the disc to receive an implant that, by way of example and not limitation, may be for fusion between body portions of the adjacent vertebrae and through the space previously occupied by the disc, each of the adjacent vertebrae to be fused including a vertebral body having an endplate outer surface adjacent the disc space, and a subchondral zone immediately internal to each endplate, the method comprising: positioning a guard into contact with the adjacent vertebral bodies for protecting access to the disc space and the adjacent vertebral bodies; and forming, through the guard, a plurality of bores to form a substantially quadrilateral space in the spine across the height of the disc space and into the adjacent endplates of the vertebrae adjacent the disc space, the quadrilateral space being formed by the removal of at least bone from at least the adjacent endplates as deep as with, and generally not deeper than, the subchondral zone of each of the adjacent endplates.
It is understood that both the foregoing general description and the following detailed description are exemplary and exemplary only, and are not restrictive of the invention as claimed.